Most commercially available MEMS microphones or silicon microphones are formed by two chips, an application specific integrated circuit (ASIC) chip and a MEMS chip attached to a substrate. These chips are generally enclosed by a conductive cover or lid. An acoustic wave is provided from an opening on a top surface of the microphone or from an opening on the substrate. Typically, in commercial applications in which the acoustic wave is input from the top (e.g., cover or lid) of the device, an acoustic back cavity is formed mainly by a volume under the MEMS chip and the substrate. By contrast, in commercial applications in which the acoustic input is from the bottom (e.g., from the substrate), the acoustic cavity is typically formed by the volume enclosed by the substrate and the cover/lid.